Densitometer having an analog computer for calculating a fraction of the total area under a curve

ABSTRACT

A densitometer which provides complete electrophoresis results on a single sheet. An electrophoresis sample is scanned by a beam of light energy. The light energy transmitted through the sample is converted to an electrical signal. An analog trace of the density profile is made on a recording chart. At the same time, the total area under the curve is integrated. After the trace and integration have been completed, the portions of the trace from which additional information is required such as area percents and protein levels are marked. The sample is rescanned and reintegrated within the selected portions of the trace. The area percents and protein levels are printed on the recording chart in digital form when the rescanning of the selected portion of the trace has been completed.

United States Patent Clifford, Jr. et al. 51 Dec. 19, 1972 [54]DENSITOMETER HAVING AN 3,185,820 5/1965 Williams et a1. ..235/l51.35 UXANALOG COMPUTER FOR 3,187,168 6/1965 Strickler ..235/183 CALCULATING AIO O THE 3,251,055 5/1966 McIntosh et al ..340/347 3,259,733 7/1966Klaver et a1 ..235/61.6

TOTAL AREA UNDER A CURVE 3,335,408 8/19670|iver................................340/l17.5

[72] Inventors: George F. Clifford, Jr.; Robert C.

wMdWlld, both of Natick, Mass. Primary Examiner-Eugene G. Botz AssistantExaminer-R. Stephen Dildine, Jr. 73 A .Clilfdlntru tsln.Ntk, 1 ssgnee s5 men c a Attorney-Richard P. Crowley and Richard L. Stevens [22] Filed:Jan. 18, 1971 57 ABSTRACT PP 107,140 A densitometer which providescomplete electrophoresis results on a single sheet. An electrophore-Rented Appuudon sis sample is scanned by a beam of light energy. TheContinuation -N 2 7 P I970- light energy transmitted through the sampleis converted to an electrical signal. An analog trace of the [1.8.Cl.....235/l5l.35, 235/6l.6 R. 235/616 A, density profile is made on arecording chart. At the 25 /219 QA, 346/2 30 same time, the total areaunder the curve is integrated. [SI] Int. Cl. ..G0ld 1/04 Aft th e andintegration have been completed, Field 9 /6 -6 A the portions of thetrace from which additional infor- 235/151.3; 250/219 QA, 222 R. 22 PCmation is required such as area percents and protein levels are marked.The sample is rescanned and rein- [56] inferences Cited tegrated withinthe selected portions of the trace. The UNITED STATES PATENTS areapercents and protein levels are printed on the recording chart indigital form when the rescanning of 2,834,247 5/1958 Pickels .356! 199the selected portion of the trace has been completed. 2,872,l06 2/1959Steele 235/6115 B 3,098,689 7/1963 Caflish et al....... ..........346/13X 27 Claims, 17 Drawing Figures T T T THE. "5 T T OPTICAL AMPLIFIERINTEGRATOR SYSTEM I AND SIGNAL AND F 3 I CONDITIONING SCALER I I I v IMODE I I SELECTION l L i I ANALOG PEN UNIT DIGITAL PRINTNG RECORDERCONTROL DRIVE SYSTEM FIG. 8 FIG. 7 FIG. 6

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PATENTEnuzc 19 m2 3. 706,877

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INVENTORS GEORGE F. CLIFFORD JR. BYROBERT C, WOODWARD uru/(7 i wfir, .u

ATTORNEYS PATENTEUBEB 19 m2 3 706; 8 77 SHEET 09 0F 1 1 UP DOWN COUNTER84 FIG. l5

INVENTORS GEORGE F CLIFFORD JR.

ROBERT C WOODWAR D ATTORNEYS DENSITOMETER HAVING AN ANALOG COMPUTER FORCALCULATING A FRACTION OF THE TOTAL AREA UNDER A CURVE CROSS-REFERENCETO RELATED APPLICATIONS This application is a continuation-in-part of[1.8. Ser. No. 27,067, ELECTROPl-IORESIS DENSITOMETER MODEL 345, filedApr. 9, 1970.

BACKGROUND OF THE INVENTION Zone electrophoresis has been used inclinical laboratories and where used, there has always been a need totranslate a quantitation of an amount of material such as, for example,dye stained protein to a report form.

Prior methods and equipment used for density determinations of the dyedstrip have been unsatisfactory for producing quick and accuratelaboratory results. For example, one method which has been used involvescutting strips into different sections and then eluting the dye fromeach of the sections. After extraction of the dye, the optical densityof the eluting solution is measured and the resulting values are plottedon a curve as a function of the distance along the original strip. It isclear that this method is time-consuming and requires many laboratoryoperations. Another method which has been used for this purpose is tosaturate the electrophoresis strip with an oil to make it moretransparent. The paper is passed over an illuminated slit and the amountof light passed through the paper is measured by suitable electricmeans. Again a curve is obtained as a function of distance along thepaper strip. This method has the disadvantage that any variation inoutput of the light source leads to error in determination of thedensity. Still another method currently employed, see for example, US.Pat. No. 2,834,247, employs a mechanical ball and disc integrator whichtraces a series of pips under the densitometric trace. Each piprepresents a defined amount of area under the densitometer profile. Theoperator then determines where components started and stopped, countsthe pips under each peak, totals all the pips, and then calculates anarea percent value. A further method employed is to use an electronicvoltage-to-frequency converter to activate solenoids which draw areapips under the curve trace. A still further method used is to scan theelectrophoresis pattern repetitively sensing the transmitted light andprojecting the density profile on a cathode ray tube. The operatoradjusts the base line, sets gates to cause a total area integral of thepattern, and adjusts a meter to read 100. The integration gates are setfor in dividual peaks and the operator reads the area value from themeter. However, with this method no record is made of the decision bythe operator on which valleys were selected for the particular areapercents. All of the above methods each have distinct disadvantageseither by being too time-consuming or too inaccurate and furtherrequiring translation of results to a final report form.

SUMMARY OF THE INVENTION We have developed a unique apparatus and methodwhereby complete electrophoresis results can be provided on a singleform and which apparatus and method eliminates the necessity of themanual recording of data. In our invention the electrophoresis stripmaterial is scanned and the light transmitted through the sample isreceived by a photometer. This transmitted signal is generally directlyproportional to the amount of the light transmitted through theelectrophoresis strip. An analog trace of the pattern is recorded on achart. At the same time the profile is being recorded, the area underthe profile is integrated and this value is stored. The operator throughmarking the chart on which the profile is recorded selects portions ofthe profile from which portions the material amount levels and areapercents are to be determined. The total material in the sample say forexample, the total amount of protein, is stored in a calculation systemin the densitometer through a digital dial. The pattern is rescanned andwhere the markings the operator has made are detected, the area percentsand material levels are printed in digital form directly on the chart.After rescan, the operator on one chart or sheet has all the informationthat is required in final form.

Briefly, our invention comprises a source of radiant energy (wave orparticle) such as light energy which may be ultraviolet, infrared,white, and of any wave length which light energy is formed into a beam,such as by passage through a lens system and then focused on the sampleand limited as by passage through a slit. The sample to be analyzedwhich may be transparent, translucent or a semiopaque materialcontaining material to be analyzed quantitatively or qualitatively,which permits variations in passage of the energy through the sample toaid in sample analysis. For example, an electrophoresis strip is exposedto a beam of light energy which may be employed in the sample byreflectance, transmission, fluorescence, or quenching; that is, throughan absorbtion of light. The light emerging from the sample is receivedon a suitable receptor such as a photometer, for example a photocell,photomultiplier, photo-diode, etc., where the signal is converted to anelectrical signal. This electrical signal is then transmitted to afunction generator which converts the signal from the sample to a levellinearly related to the amount of material to be analyzed in the sample.The conversion of the signal from the light receiving means may belinear, logarithmic, log inverse, linear inverse, or some other hybridfunction. Other types of samples which themselves provide a source ofradiant energy may be successfully used with the invention in which aseparate source of energy is not required, such as radioactive samples.For example, materials such as proteins may be tagged with radioactiveparticles in which case the tagged material itself is the energy sourceand the slit needs only to reflect or absorb a radioactive materialwhereby the photomultiplier is only looking at one section of thepattern at any given time. This technique may also be employed withtagged amino acids.

After passing through the function generator, the signal is recorded inthe function desired as a profile trace. Simultaneously, with therecording of the profile trace, the signal is converted to a pulse trainthe frequency of which is related to the signal level and the pulses areaccumulated and stored thereby integrating the area under the profiletrace. After the density profile has been traced and the area under theprofile integrated, a portion of the trace profile from which additionalinformation is desired, such as the particular area between selectedportions, is then marked. The sample is rescanned over the portionscanned previously. The integrated rescan signal is then compared withthe accumulated scan signal, the values compared, and the area percentscomputed as well as the material amounts. Upon command, the desiredinformation is then recorded directly on a medium such as a chart.

Other distinct advantages of our invention are the ability to record thedensity profile in one function, say for example in linear inverse, andto integrate in another function, say for example log inverse; or torecord the trace profile and integrate in the same function. Also,because the printing of the information on rescan is on the samerecording form as the indications made by the operator, all pertinentinformation is directly printed out on the same report form.

Because the majority of clinical laboratories are involved in programsleading to the use of computers for compiling laboratory results bypatient, computer compatibility has also been designed into thedensitometer. The area percent information and the percent proteinvalues are both held in binary coded decimal (BCD) form. On receiving apulse from the computer, the information can be transferred to thecomputer and thence to a memory block to be held until the computercalls for the information on that patient. A minimum of computer memoryis required since the need for point-by-point logging of the densityprofile is completely eliminated.

Further, since the densitometer has its own calculation capability itdoes not depend upon a computer to derive area percents or percentmaterial values, complete results are obtainable whether or not thecomputer is in service. Inspection of the chart containing the densityprofile provides immediate information such as to the identification ofalbumin and the various globulins. In providing a means for locatingfractions along the density profile, the pattern being scanned, thesample, and the recorder are both driven with stepping motors. Bycounting the steps to each valley, location information is providedwhich can be used in a simple computer program to identify fractions.

Since most cellulose acetate and gel patterns can be preciselyquantitated by integrating in log inverse, this is generally thepreferred embodiment or method of operation in the densitometer.However, if the amount of light absorbing material does not increaselinearly with optical density, the densitometer is also provided withmeans to perform the integration linearly in a function such as dyeconcentration on filter paper or such other function as defined by theuser.

In our invention, the analog system of a densitometer has been combinedwith the digital calculation and printing capabilities of a digitalcomputer to provide on a single report a density profile of theelectrophoresis pattern, marks such as by punches or from an electronicvalley sensing system indicating how the pattern was divided forcalculation purposes, a digital value of area percent printed on thechart for each peak or group of peaks in the pattern, means to enter thetotal amount of sample material into the densitometer and to print thatamount of digital form on the chart, and the capability to multiply areapercent times the total material and to print the amount of eachfraction selected. Our invention eliminates the necessity of meterreading and interpolation errors as well as transcription errors andcombines an analog and digital presentation for obtaining the greaterprecision of the digital system for calculation of results and further,it is not limited to a certain number of peaks by number of analogmemory devices. The marking system employed is advantageous in that itobtains correct results from all serum protein and lipoprotein patternswhich often have shoulders and points of inflection which cause anelectronic valley sensor to divide patterns into fractions which are notrelated to the actual material distribution desired.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of theinstrument;

FIG. 2 is a block diagram of the basic sections of the instrument;

FIG. 3 is a partly schematic and partly sectional view of the opticalsystem of the invention;

FIGS. 4a and b are plan views of the sample holder;

FIG. 5 is a schematic illustration of the amplifier and signalconditioning, mode selection, and integrator and scaler portions of theinvention;

FIG. 6 is a schematic illustration of the digital printing drive systemof the invention;

FIG. 7 is a partly block diagram and plan view of the control section ofthe invention;

FIG. 8 is a plan view of the analog pen recorder section of theinvention;

FIGS. 9a and b are schematic illustrations of the movement of the bridgeassembly during the slew, scan, pretravel and rescan cycles;

FIG. 10 is a plan view of the valley sensing system;

FIG. 11 is a block diagram of the functional elements of the invention;

FIG. 12 is a circuit diagram of the print control;

FIG. 13 is a circuit diagram of the unit control;

FIG. 14 is a diagram of the pretravel circuit; and

FIG. 15 is a circuit diagram of the up-down counter.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The instrument 10 is shown inFIG. 1 and includes two consoles I2 and 14. The entire system is alsoshown in block diagram form in FIG. 2. Each major section of the systemwill be described individually prior to the description of the entiresystem in a working embodiment.

OPTICAL SYSTEM The optical system is shown in greater detail in FIG. 3and comprises a white light source 22 which is powered by a regulatedpower supply 24. The light source as shown is a standard lamp operatedat a fixed temperature of about 2,700I(. If desired to ensure that thelight intensity is constant, a receptor 25 shown in the dotted lines maybe utilized to regulate the power supply based on the intensity of thelight received. Light energy from the source passes through a heatabsorbing or reflecting lens 26, condensing lens 28, filter 30, deflectsoff a mirror 32 and then passes through an aperture 34.

If desired depending upon the sample being analyzed, energy sourcesother than white light may be used such as ultraviolet, infrared, etc.,and the wave lengths of the incident energy may vary as selected byfdters, monochromators, or lenses used. Further, light energy may bemeasured emerging from the sample by reflectance transmission,fluorescence, or quenching.

Referring to FIGS. 3, 4a and b, an electrophoresis sample 36 is placedin a unique holder 37 which employs a flexible magnetic mat 38 such asvinyl ferrite in combination with a magnetizable material 40 such assteel. The holder communicates with a stepping motor 44, whichreciprocates the holder along a fixed path during the scan and rescancycles. The stepping motor also communicates with the unit control 80 asshown in FIGS. 7, 11, and E3. The use of the magnetic mat to hold thesample in place facilitates insertion and adjustment of the sample inthe holder while firmly holding the sample in place during the scanningand rescanning cycles. A termination switch 46 which can be adjusted tocoincide with one end of the portion of the sample to be scanned,terminates movement of the sample holder at the end of the scan cycle.

A photocell 48 such as a vacuum photodiode receives the lighttransmitted through the sample and converts the signal to a currentproportional to the energy emerging from the sample being analyzed.

INTEGRATION Referring now to FIG. 5, the current from the photocell 48of FIG. 3 is transmitted to an amplifier 50 such as a variable gainamplifier. One of a plurality of function generators such as a loginverter 52, linear inverter 54, or a hybrid function 55, receives thesignal from the amplifier $0 and transmits the signal at a dift'erentlevel to an analog recorder 56, such as a servoarnplifier.Simultaneously the signal is also transmitted to a vottage-to-t'requencyconverter 57. As shown, if desired, a signal may be transmitted directlyrather than passing through one of the function generators. A pluralityof cascaded binary-coded decimal decade counters within the totalpattern integrator 58 or total area counter accumulate, totalize, andstore the pulses received from the voltage-to-trequency converter 57whereby the total area under the density profile trace on the recordingchart as shown on FIG. 8 is integrated. Upon rescan, certain selectedportions of the density profile trace are selected for analysis and thesample rescanned whereby the area under the selected portion isreintegrated, and the pulses accumulated in the peak integrator 59 orrescan counter. These rescan pulses are compared in the comparator 66against the pulses stored in the total pattern integrator $8. The totalpulses in the total area counter are digitally divided by rm to provideunits or values of comparison of 0.1 percent of the total area under thecurve. When the rescan pulses reach a predetermined level correspondingto 0.1 percent of the total area, the information is transmitted to thedigital printing and drive system shown in FIGS. 6 and 12. After eachtransmittnl of 0.1 percent pulses to the data selectors, the comparatorresets the rescan counter 59 and the pulses are again accumulated untilthey reach a value of 0.1 percent of the total area as determined by thecomparator. Again the information is transmitted to the data selectors.This cycle continues throughout rescan while periodically the valleysensing system will command the printing and drive system to print thedesired information as will be described later.

As shown in FIG. 7 and- FIG. 5, the operator may integrate in onefunction such as log inverse, and record in another function such aslinear inverse, during a scanning cycle, or if desired, through theseiection of the appropriate functions the integration and recording mayboth be accomplished in the same function or either function may beaccomplished directly.

DIGITAL PRINTING AND DRIVE SYSTEM Referring to FIGS. 6 and 11,. thedigital printing and drive system comprises a plurality of data selectorcircuits 620, b, and c which communicate with a plurality of printadapters. 64a and b which transmit the signal. received from the dataselectors to the count wheels and actuate the count wheels in therecording system. A material multiplier 66 or milligram adapter whichcomprises a binary coded circuit stores the total amount of proteinwhich value is inserted into the multiplier by the operator through thedigital dial 78 shown in FIGS. 7 and H. The 0.! percent signals from thecomparator flow in two directions, one directly to the data selectors incombination with the prim adapter 640, and the second to the miiiigramadapter 66 and then to the data selectors associated with printadapters- 64b. The material multiplier digitally multiplies the percentsignal times the total material value as dialed-in prior to transmittalto the data. selectors.

As will be described in detail, upon receipt of a command from thepretravel circuit shown in FIG, 14,. the stored value of total materialis printed on the recording chart prior to rescan. Upon receipt of acommand trom the valley sensing system, the area percent and the areapercent times total material corresponding to the selected portion ofthe chart is printed on the chart.

The print control circuit 68 is adapted to receive commands from theunit control shown in FIG. I and the valley sensing system 101 shown inFIGS. 1!, l2, and 13.

UNIT CONTROL Referring to FIGS. 7, It, and 13, the unit control 80comprises a control panel 10 having a series of switches for commencingoperation of the instrument and as shown includes the reset, scan andresean switches and valley selection indicator. An integrator dial 72and recorder dial 14 select the recording and integration functions aswas described for FIG. 5. Also on the front panel, is a scan lengthswitch F6 which determines the ratio of the speed of motion ofthepattern tothe speed of motion. of the bridge in the recorder. This speedratio controls the amount of total motion of the pattern whichcorresponds to the bridge moving across the usable portion of the chart,and the scan length switch is calibrated in these distances.

In communication with the control panel is the unit control 80 alsoshown in greater detail in FIG. 13. A pulse generator 82 which isdisposed in the control 68 communicates with the unit control 80 andprovides a pulse train for driving both the stepping motors 44 and shownas drives in FIG. 11 for the scanner and recorder respectively. Toensure that the movement of the bridge carrying the pen, and the holdercarrying the sample being scanned each move precisely the same distanceduring scan and rescan, an up-down counter 84 counts the pulsesgenerated during scan and rescan to terminate the rescan mode when thesame section of the pattern originally scanned has been rescanned. Thisensures that the total area integrated is identical in both scans.

A slew switch 83 moves the recording pen to the starting position priorto the actuation of the scan cycle. A pretravel circuit 86 on rescanmoves the bridge carrying the pen recorder, count wheels, and valleysensing system, a predetermined distance prior to actuating rescan ofthe sample to compensate for a mechanical offset of the pen 98 andvalley sensing system 101. This circuit also controls the print-out ofthe total amount of material which is stored in the material multiplier.

RECORDING SYSTEM Referring to FIGS. 8 and 9a and b, the analog penrecorder comprises a bridge assembly 92 which includes two sets of countwheels 94 and 96 which communicate with the print adapters 64a and 64bwhich wheels record the area percent of selected portions of the densityprofile trace and the material protein levels. A pen recorder 98 engagesa recording chart 100. The trace of the pen along its x axis iscontrolled by the movement of the bridge driven by the stepping motor90. The amplitude or movement of the pen along the y axis is controlledby the analog recorder whereby the pen position is directly proportionalto the signal selected for recording. The recording pen 98 is slidablyengaged within the arm 102 of the bridge assembly 92.

A valley sensing system 10! as shown in FIG. 10 comprises a light source104 and a photoresistor 106 disposed within the arm which source andresistor are located on either side of the recording chart 100. Whenactuated on rescan, the valley sensing system senses the marks made inthe recording chart by the operator and transmits a signal to thedigital printing drive system. If desired, in lieu of the light andphotoresistor, other valley sensing systems such as an electronic valleysensing system may be used.

FIG. 8 is a top plan view of the travelling bridge and recording chartafter scan and rescan. A stepping motor 90 which is preferably driven bythe same pulse train as the scanner stepping motor 44 moves the bridgeassembly 92 along a fixed path during the scan and rescan periods oftravel. The line of digits 112 represent area percent and the line ofdigits I14 represent the material level accumulated to each mark on therecording chart.

The recording chart 100 is carried in a unique holder 124. Each end ofthe recording chart is magnetically held down by magnetic strips 116which overlay the chart and magnetically engage the steel surface of theholder.

THE OPERATION The operation of our invention will be described inreference to an analysis of an electrophoresis strip in which variousprotein fractions of a blood sample are distributed along the strip.

Initially the power of the instrument is activated. Referring to FIGS.40 and b, a sample 36 is placed on the steel holder 40 and the magneticmat is placed over the sample and magnetically secured to the steelplate 40. The slit 34 through which the light energy passes is adjustedto the desired width. The termination switch 46 shown both in FIGS 40and b and FIG. 3 is then set manually to limit the movement of thesample being scanned during the scanning cycle and generally is locatedabout at the end of the protein pattern. The sample holder is adjusteduntil the slit is under a clear portion of the pattern wherein a maximumamount of transmission of light is passing therethrough. The lightenergy created by the lamp passes through the various filters and lensesis focused on the pattern and passes through the adjustable slit 34 andreceived on the phototube 48 which communicates with the amplifier 50.The variable gain amplifier 50 is adjusted until the pulses received onthe voltage-to-frequency converter are as close to zero as possible.This may be determined by visual electrical means such as a flashinglamp 16 which is shown on the console 14 in FIG. I and in FIG. 11. Thetermination switch for the bridge assembly (not shown) may also beadjusted to limit the movement of the bridge during scan.

A recording chart is secured across a flat surface as shown in FIG. 8 bymagnetically engaging the edge of the paper to a holder through the useof a magnetic strip 116 which cooperates with the magnetic holder alongthe edge of the flat surface.

The function in which the trace is made and in which the area under theprofile is integrated is then made. As shown both the integration andthe profile trace will be done in log inverse functions. On therecording switch it is possible to vary the amplitude of the tracepattern at a ratio of two to one by selecting the 1.5 or the 3.0 opticaldensity (O.D.) level. That is, if the log inverse function is directedto the 3.0 0.0. level, then the amplitude of the trace on the recordingchart will be half than that if the selection had been at the 1.5 O.D.level.

Of course, it should be understood that, if desired, recording in linearinverse would expand the small peaks making it possible for the operatorto make better decisions on the proper selection of valleys betweenpeaks while integration may be performed in a log inverse function tocorrectly quantify material.

Referring to FIG. 7, the scan length selection switch 76 is set todetermine the length of the scan of the trace of the pen in reference tothe scan of the sample. The scan length determines the ratio of speedsof the bridge assembly to the sample holder. That is, as shown, it isset at 50 which means that the speed at which the bridge assembly isdriven will be four times the speed at which the sample moves from itsinitial position until the scan cycle is stopped by actuation of thetermination switch 46. The length of the scan of the sample isdetermined by the location of the termination switch after the samplehas been inserted in the holder. The length of the trace across thechart along the x axis is determined by the scan length control which isdependent upon the ratio of speeds between the stepping motor drivingthe sample scanner and stepping motor driving the bridge assembly. Thetermination switch 46 for the bridge assembly may be employed in lieu ofthe termination switch 44.

The amount of material in a particular sample which in this instance isthe total amount of protein in the sample is then dialed in the digitaldial manually 78 and stored in the milligram adapter as shown in FIG. 6.Referring to H0. 13, if the reset lamp is not on, the reset switch (lampswitch) also shown on the control panel 70 in FIG. 7 is actuated andsets flip-flop 115a to the one state via gate lllc. This energizes thereset lamp on the control panel 70 and holds the instrument in the resetmode. The slew switch 83 is actuated to move the bridge assembly intoposition as shown in FIG. 9a through the slew distance. The zeropotentiometer connected with the amplifier 50 is adjusted to bring thelight 16 to a flashing condition. Also, when the rescan switch isactuated, all stages of the up-down counter 84 shown in FIG. 15 are setto by gates 511a and Sllb.

When the slew switch 83 is actuated, the bridge assembly or recordermoves the slew distance A as shown in FIG. 9. Referring to FIG. 13, gate21 la is enabled by the actuation by the slew switch 83 on the controlpanel to manually position the recording assembly to the right as shownin FIG. 9a.

The scan switch on the control panel 70 is then actuated and since theswitches on the control panel are light switches, the actuation of theswitch is indicated by the light as shown in FIG. 13.

Actuation of the scan switch on the control panel after the bridgeassembly has moved its "slew" distance with flip-flop 115a in the onestate sets flip-flop 1151) to its one state and resets flip-flop [a toits zero state through gate 112a. Flip-flop llSb enables flip-flop 1160to be set to its one state through gate 11% immediately after flip-flop115k has been set. The output of gate ll2b also resets flip-flop llSbthrough gates HM and 1 130. When either flip-flops 1 15b or 1160 are inthe one state the scan lamp is energized via gate 113d. Flip-flop 116athus holds the instrument in the scan mode until it is reset by a signalfrom the scanner termination switch 46.

The logic level generated by gate 211a controls the direction ofrotation of the stepping motor 90 to drive the bridge assembly. Thebridge assembly stepping motor drive signal which is a 10Ms square waveis obtained from gate 211d. The logic levels generated by gates 211a and2l0c control the direction of rotation of the stepping motor 90 vialogic circuitry in the stepping motor drive unit. The motor drive signalis derived from the square wave clock located in the print control unitthrough gates 21 lb or 2110. During the scan cycle, gate Zllb is enabledthrough gate 2110 by flip-flop 1160 which is in its one state. Gate211:: generates a go right command. As shown in FIG. 90, this would movethe bridge assembly to the right through its scan cycle.

The scanner drive motor or stepping motor 44 is controlled in similarfashion when the instrument is in the scan mode. Flip-flop 1 16acommands the scanner holding the sample to go right" during the scanmode (flipflop ll7b commands the scanner to "go left" during the rescanmode) via logic circuits the same as those employed for the bridgeassembly stepping motor drive and generally located in the steppingmotor drive unit 44. The period of the scanner motor drive pulses 44 ismanually selectable in order to provide three scan langths: 25centimeters, 50 centimeters, and 100 centimeters as shown in FIG. 7. Thescan length switch 76 on the control panel and as shown in FIG. 13selects gates 213a, 213b, or 2130 (via inverters 212b, 212e, and 2124)for the appropriate scanner motor drive signal. The three availablesignals are derived from the lOMs clock and the outputs of the two-stagecounter flip-flop 118a and flip-flop 118i; which provides square wavesof 20Ms and 40Ms. The outputs of gates 2130, 213b, and 2l3c are appliedto gate 214d which during the scan cycle is enabled by flip-flop 1164.(During the rescan cycle, gate 214d is enabled by flip-flop 117k.)

When the scan switch is actuated, the stepping motors 44 and are drivenby the pulse generator 82 whereby the stepping motors move the scannerholder 40 transversely to the beam of light passing through the slit 34and move the bridge assembly 92 along the x axis of the recording chart100. The variations in light transmitted through the sample are receivedby the photometer 48 and transmitted to the amplifier 50. The signal isconverted to a selected integrator function log inverse as shown andsimultaneously converted to a selected analog recorder function, loginverse as shown. The density profile trace of the sample being scannedis recorded on the recording chart by the pen recorder 98. The pulsesfrom the voltage-tofrequency converter are serially accumulated in thecascaded binary coded decimal counters in the total pattern integrator58 and totalized while the sample is being scanned. When the sampleholder 40 actuates the termination switch 46, a signal is transmitted tothe unit control 80.

During the scan cycle, 40Ms clock pulses are applied to the up-downcounter 84 and during this cycle flipflop 116a commands the up-downcounter 84 to count up. The pulses during scan are accumulated to somearbitrary count depending upon the scan period. Referring to FIG. 15,flip-flop 116a of unit control through gates 214a and 2l4b enables gate51% and gate 512a is disabled via gates 501a and 5011) respectively.When flip-flop 513a responsive to 40Ms pulses from the unit controlchanges from its l" to its 0" state, a carry pulse is transmittedthrough gates 5l2b and 5120 to the input of flip-flop 5l3b. [n a likemanner each of the nine stages as shown receives an input pulse from thepreceding stage when the latter goes from l to 0". This results in anup-counting mode. Also, during the scan cycle, the pretravel counter 86receives 40Ms pulses from gate 2l4c which is enabled by flip-flop 4170.

Referring to FIG. 13, the termination switch 46 signals through gates1120, 113b, and 113:: that the scanner has reached the end of travel inthe scan direction. The output of gate l 12:: sets flip-flop ll6b to itsone state and thus establishes the select valleys mode and terminatesthe scan mode. Although the scanner limitation or termination switch hasbeen shown, a similar termination switch which may be physicallyadjusted to limit the travel of the bridge assembly rather than thescanner may be employed in this instrument which bridge assemblytermination switch would be responsive to engagement by any desiredportion of the bridge assembly. As shown in FIG. 13, the terminationswitch (recorder or scanner) is designed so that a switch may beemployed as shown for the scanner or for the bridge assembly or for bothand the unit control would be responsive to the first received signal.The output of gate 112c also sets flip-flop 116k to its one state whichestablishes the select valley mode and resets flip-flop 116a.

The select valleys indicator or light on the control panel is actuatedand the operator at this time selects the valleys on the profile tracebetween which valleys the area percent and protein levels are to bedetermined. As shown in FIG. 8, these valleys are selected by physicallypunching slots in the edge of the recording chart 100. The selectvalleys lamp is controlled by flip-flop I161).

The pretravel counter 86 which is shown in schematic form in FIG. 14 ispreset to a determined number (determined during final tests) via gates419a and 41% by a signal from the unit control when the select valleysswitch is actuated. The preset number is determined by wiring jumpers tothe terminals as shown. During rescan l or pretravel, clock pulses fromthe unit control are applied to the input of the counter. The counter iswired to count down from the preset number. At the count of 010000(i.e., decimal 2) gate 412 generates the command which causes the valueof the material amount level which was stored by the digi-switch to beprinted on the recording chart. At the count of l000000 (decimal l) gate411 generates the end of pretravel signal which signal initiates therescan 2 mode and terminates the pretravel or rescan 1 mode.

After the indications have been made on the recording chart 100selecting the valleys to be examined, the rescan switch is actuatedwhereby flip-flop 117a is set to its one state via gate 112d. Theactuation also resets flip-flop ll6b to its zero state. Flip-flop 117aestablishes the pretravel or rescan 1 mode. Referring to FIG. 9b, thismoves the bridge assembly I01 the pretravel distance C while the scannerremains stationary. That is, the stepping motor 90 drives the bridgeassembly. The pretravel counter which previously received pulses fromgate 2140 which was enabled by flip-flop 117a is designed to count downa predetermined number of pulses during this pretravel cycle to controlthe movement of the bridge assembly the distance C shown in FIG. 9b. Aspreviously described, flip-flop 215 is set to its one state by flip-flop1170 which causes gate 2l0c to generate a go left" command and alsoenables gate 21lc to provide the motor drive pulses. When the rescanswitch is actuated, the print control 68 receives print commands fromthe pretravel counter 86, for example, the total material amount in thetotal material digi-dial 78 upon command from the pretravel counter, thevalue stored in the digi-dial 78 is transferred to the decade countersin the data selectors 620, b, and c in combination with the printadapter 64b. The command from the pretravel counter enables gate 312a ofFIG. 12 to trigger the circuitry which transfers the data to be printedfrom the data selectors to the print adapters. Flip-flop 310a enablesgate 306!) to transmit print pulses to the printer adapters to the countwheels, and then to the printer solenoid command at the appropriatetime. This particular circuitry will be described in detail during therescan 2 cycle of the instrument.

The amount of material in the digi-dial is printed as shown on FIG. 8 bythe count wheels 96. Upon completion of the pretravel cycle when thepretravel counter has counted down to zero or decimal one, a signal fromgate 411, FIG. 14, is gated to gate 212a of the unit control. This setsF/F 1 17b to its one state and causes the scanner motor drive togenerate a "go left" command. Also, through gates 214a and 2141: itcauses the updown counter 82 to count down at the termination of thepretravel. The bridge assembly continues to move and the updown countercommences to count down and simultaneously the stepping motor 44 isactuated and the sample rescanned and curve reintegrated as describedduring the scanning cycle.

Referring to FIG. 15, gate 512a is enabled from gate 2141: and gate512!) is disabled whereby flip-flop 513i: receives an input pulse whenF/F 513a goes from 0" to 1" and similarly for other stages. In this modethe counter counts down from the count which was accumulated in scan.When the count reaches zero, gate 515 produces an output to the unitcontrol to gates 1110, lb, and lllc which sets flip-flop 115a to one,"its reset condition, and resets flip-flop 117!) to its zero state toterminate the drive of the stepping motor 44 and to end rescan two. Thisstops scanning motor 44 and reintegration of the sample. The bridgeassembly continues moving the distance E shown in FIG. 9b until itstrikes the left termination switch after moving the slew distance.

On rescan, the pulses received on reintegration are transmitted to therescan counter and accumulated. Referring to FIG. 11, the pulses fromthe voltage-tofrequency converter received on rescan are accumulated inthe rescan counter 59. These pulses are continuously accumulated andcompared in the comparator 60 against the total accumulated pulses andin total area counter 58. The pulses initially received in the totalarea counter are divided by 1,000 to produce 0.1 percent pulse values.Each time the rescan counter 59 counts pulses corresponding to 0.1percent pulses as determined by the comparator 60 this information istransmitted directly to the decade counters in the data selectors 62a,62b, and 62c.

As shown most clearly in FIG. 11, the pulses are serially accumulated inthe decade counters of the print modules directly from the comparator.The same signal or value from the comparator each time the 0.1 percentpulse level is reached is transferred directly to the milligram adapter66. The milligram adapter multiplies the percentage of each signalreceived by the total amount of protein which was dialed in by thedigi-dial 78 and serially transfers this information to the decadecounters associated with the data selectors of the material printmodules After each transfer of the 0.1 percent pulse to the appropriatedata selectors, the rescan counter is automatically reset by thecomparator. In the rescan mode the transfer of information to the dataselectors continues and is accumulated in both sets of the decadecounters until such time as the first mark made on the recording chartis sensed by the photocell of the valley sensing system. When thephotocell 106 in the valley sensing system which is contained within thearm of the bridge assembly 92 senses the first mark by the operator, theinformation is printed directly on the recording chart 100 by the countwheels 94 and 96.

Referring to FIG. 12, the signal from the photocell which senses themark which was punched by the operator to select the valleys is appliedto amplifier A8. When the punch mark is sent, the output of A8 setsI060ll 0542 flip-flop 3100 to its one state via gates 308, 3010, 3020and 302d. Gates 312a and 31% as shown form a pulseshaping network. Theoutput of gate 302d also enables the gate 3120 to trigger the circuitrywhich transfers data to be printed from the data selectors to the printadapters. This circuitry which comprises flip-flops 316a, 316b, andgates 312a, 312b, 312e, 311e, 311d, 306a, 3150, 315b, and 315s developsa 0.4 microsecond transfer command to the data selectors followed by a0.4 microsecond clear command. The data input lines to the dataselectors are inhibited during the clear and transfer period.

Referring to FIG. 11, when the output from gate 302d enables gate 312ato trigger the circuitry as described, referring to the data selectors62a, 62b, and 62c, the information accumulated in the decade counters isallowed to pass through the transfer gates and into the binary codeddecimal to serial converters which comprise the print adapters.Specifically, for the 0.1 percent pulses transmitted directly to thepercent print modules, the information accumulated on the decadecounters flows through the transfer gates and into the serial convertersor print adapters 64a. Similarly, the same occurence takes place atprint adapters 64b where the information which was multiplied in themilligram adapter and accumulated on the decade counters in transferredto the serial converters of the print adapters 64b.

Flip-flop 310a enables gate 306b to transmit print pulses to the printadapters. Flip-flop 3100 also enables gate 314a to transmit clock pulsesto the input of a fivestage counter which comprises flip-flops 3050,305b, 3090, 30%, and 31%. The fivestage counter controls the timeinterval during which the print pulses and reset pulses are applied tothe print adapters. This counter also generates the print or solenoidcommand at the appropriate time. ln the select valleys mode reset pulsesare generated on command from the unit control via gate 314d. At theconclusion of the print cycle, flip-flop 3160, 316b and 310a are resetto zero by a signal from gate 313 through gates 315d, 315e, and 315Flip-flop 310a then resets the five-stage counter. The print control isthen ready to receive the next command. During the rescan mode, theprint commands from the valley sense circuit are accepted only duringthis mode and this feature is controlled by gate 308. The print commandoutput code is a two-bit code generated by gates 311a and 311k.Therefore, gate 306b in timed relationship transmits print pulses to theprint adapters 64a and 64b. This information is transferred to the countwheels where the count wheels are rotated to the proper position.Subsequently, upon command from the counter, the print or solenoidcommand is made whereby the information is printed in digital form onthe recording chart 100 as shown in FIG. 8.

This rescan mode is continued and each time the valley sensing systemsenses the mark made by the operator, the accumulated information in thedecade counters is transferred to the print adapters and then printed onthe recording chart. The rescan and reintegration of the sample and themovement of the bridge assembly is continued until the movement of thescanner drive ceases when the counter 84 has counted down. The bridgecontinues travel on rescan whereby a left recorder limit switch (notshown), which is physically set to engage the bridge assembly at the endof the slew distance, resets flip-flop 215 comprised of gates 215a and2l5b. This in turn inhibits the recorder motor drive pulses throughgates 215e, 215d, 210e, 2111:, and 211d. The recorder stepping motordrive signal which is a 10Ms square wave is obtained from gate 211d. Asmentioned above, in the rescan mode flip-flop 215 of the unit control isset to its one state by flip-flop 117a. This causes gate 2100 togenerate a "go left command and also enables gate 2110 to provide themotor drive pulses.

Similarly, the scanner drive stepping motor 44 is controlled in similarfashion. Flip-flop ll7b commands the scanner to "go left" during therescan mode via the logic circuits located in the stepping motor driveunit 44. Referring to FIG. 9b, the bridge assembly is now in theposition indicated by the dotted line and prior to analyzing the nextsample, the slew switch is actuated to bring the bridge assembly and penback to the beginning of the scan cycle.

Having described our invention, what we now claim l. A densitometerwhich comprises in combination:

a. a source of energy;

b. means to expose a sample to be analyzed to said energy;

c. means to cause the scanning of the sample by relative movementbetween the sample and said enerd. means to convert the energy emergingfrom the sample to an electrical signal;

e. means to display a selected signal in analog form;

f. means to integrate a selected signal;

g. means to select a portion of the analog form from which additionalinformation is desired;

h. means to cause the rescanning of the sample and to integrate thesignal received;

i. means to compare the integrated rescan signal with the integratedscan signal; and

j. means to record the compared signals in digital form.

2. The densitometer of claim 1 wherein the source of energy is lightenergy and which includes means to focus said light energy as a beam,the means to expose the sample to the beam of light energy includes anaperture therein whereby the sample may be placed on a support means andthe beam of light energy adapted to pass through said aperture, and.wherein the means to scan the sample includes means to drive thesupport means along a predetermined path.

3. The densitometer of claim 2 wherein the support means includes aholding means having a flat surface thereon, said surface beingcharacterized by a slot therein and being formed of a magnetizablematerial, and further wherein a magnetic mat having an aperture slittherein is secured to the flat surface of the holding means whereby thesample is placed on the flat surface of the holding means and themagnetic mat engages the magnetizable material thereby holding thesample firmly in place.

4. The densitometer of claim 2 wherein the means to drive the supportmeans includes a motor means adapted to operate at a selected constantspeed which reciprocates the support means between preselectedpositions.

5. The densitometer of claim 1 wherein the means to convert the lightenergy to an electrical signal includes a photometer whereby the energyis converted to current and said current is transmitted to an amplifierwhose output signal is voltage,

wherein the means to display in analog form includes a servomechanism incombination with a recording stylus adapted to trace a profile,

wherein the means to integrate includes a voltage-tofrequency converterand a plurality of BCD cascade counters,

wherein the means to select portions of the profile trace to beintegrated on rescan includes means to mark a medium on which thedensity profile trace is formed, and

which includes means to control the scan and rescan cycles.

6. The densitometer of claim 1 wherein the means to rescan the sampleincludes holding means and drive means to move the holding means along apredetermined path;

wherein the means to integrate the signal during rescan includes meansto accumulate a plurality of pulses on BCD cascade counters,

wherein the means to compare the rescan signal with the totalaccumulated signal includes means to calculate the percent of rescansignals compared against the total accumulated signal, and

wherein the means to record the signal in digital form includes printmeans.

7. The densitometer of claim 6 wherein the means to calculate the areapercent includes a digital divider.

8. The densitometer of claim 1 wherein the sample being analyzed is athin layer chromatography plate.

9. The densitometer of claim 1 which includes means to definepreselected areas of the analog trace.

10. An improved densitometer which comprises in combination:

a. a source oflight energy;

b. means to form a beam of said light energy;

c. means to expose a sample to be analyzed to the beam of light energy;

d. means to scan the sample with the beam of light energy;

e. means to convert the light energy transmitted through the sample toan electrical signal;

f. function generator means to convert the signal from the sample to alevel related to the amount of material to be analyzed in the sample;

g. means to record the signal in analog form as a profile trace on arecording medium;

h. means to integrate the selected signal with the recording of theselected signal in analog form in communication with the functiongenerator means;

i. means to select a portion of the analog profile trace from whichadditional information is desired;

j. means to rescan the sample and to integrate the signal received;

it. means to compare the integrated rescan signal of the selectedportion of the analog profile trace with the total accumulated scansignal whereby on comparison the pulses are discharged; and

l. means to record the compared signals in digital form on the medium.

11. The densitometer of claim 10 wherein the function generator meansincludes a linear inverse converter, a log inverse converter, functionof x converter, and further includes the means to record in one of saidfunctions and integrate in that or another of said functions as desired,

wherein the medium includes chart recording means,

and

wherein the means to record in digital form includes:

l. housing means,

2. bridge means secured to the housing means and extending across thechart recording means,

3. sensing means adapted to indicate when the rescan of a selectedportion of the analog trace has been completed and pen means disposed inthe bridge means, and

wherein the chart recording means includes a chart which is magneticallysecured to a support means,

wherein the digital printing means are disposed within the housing ofthe bridge assembly and axially aligned with and spaced apart from thesensing means along the y axis of the recording chart.

[2. The densitometer of claim 11 wherein the means to compare theintegrated rescan signal against the total accumulated scan signalincludes means to calculate percents.

13. The densitometer of claim 12 wherein the means to calculateincludes:

means to store a number representing the total amount of material;

means to control the movement of the holding means and bridge assemblymeans;

means to control the selection of the information transmitted to thedigital printing means in the bridge assembly means;

means to multiply percent times the total amount of material; and

means to print the percent and the material amount for the selectedportion of the analog trace upon the receipt of a command from thesensing means.

14. The densitometer of claim 10 wherein the sample being analyzed is anelectrophoresis strip.

15. The densitometer of claim ll wherein the bridge assembly means andthe holding means for the sample are each driven by stepping motorswhich stepping motors are driven by pulses derived from the same pulsetrain.

16. A method of scanning a sample and recording the results of said scantherefrom which comprises:

a. creating a source of light energy;

b. exposing a sample to be analyzed to the beam of light energy;

c. receiving a portion of said beam of light energy emerging from thesample on a receptor;

d. converting the light energy emerging from the sample to an electricalsignal;

e. integrating the electrical signal transmitted from the receptor;

f. recording the signal from the receptor as an analog profile trace ona medium;

g. selecting a portion of the profile trace from which desiredinformation is required;

h. rescanning and integrating the sample over the desired portion fromwhich information is desired;

i. comparing the integrated rescan signal against the total integratedscan signal;

l060l l 0544

1. A densitometer which comprises in combination: a. a source of energy;b. means to expose a sample to be analyzed to said energy; c. means tocause the scanning of the sample by relative movement between the sampleand said energy; d. means to convert the energy emerging from the sampleto an electrical signal; e. means to display a selected signal in analogform; f. means to iNtegrate a selected signal; g. means to select aportion of the analog form from which additional information is desired;h. means to cause the rescanning of the sample and to integrate thesignal received; i. means to compare the integrated rescan signal withthe integrated scan signal; and j. means to record the compared signalsin digital form.
 2. The densitometer of claim 1 wherein the source ofenergy is light energy and which includes means to focus said lightenergy as a beam, the means to expose the sample to the beam of lightenergy includes an aperture therein whereby the sample may be placed ona support means and the beam of light energy adapted to pass throughsaid aperture, and wherein the means to scan the sample includes meansto drive the support means along a predetermined path.
 2. bridge meanssecured to the housing means and extending across the chart recordingmeans,
 3. sensing means adapted to indicate when the rescan of aselected portion of the analog trace has been completed and pen meansdisposed in the bridge means, and wherein the chart recording meansincludes a chart which is magnetically secured to a support means,wherein the digital printing means are disposed within the housing ofthe bridge assembly and axially aligned with and spaced apart from thesensing means along the y axis of the recording chart.
 3. Thedensitometer of claim 2 wherein the support means includes a holdingmeans having a flat surface thereon, said surface being characterized bya slot therein and being formed of a magnetizable material, and furtherwherein a magnetic mat having an aperture slit therein is secured to theflat surface of the holding means whereby the sample is placed on theflat surface of the holding means and the magnetic mat engages themagnetizable material thereby holding the sample firmly in place.
 4. Thedensitometer of claim 2 wherein the means to drive the support meansincludes a motor means adapted to operate at a selected constant speedwhich reciprocates the support means between preselected positions. 5.The densitometer of claim 1 wherein the means to convert the lightenergy to an electrical signal includes a photometer whereby the energyis converted to current and said current is transmitted to an amplifierwhose output signal is voltage, wherein the means to display in analogform includes a servomechanism in combination with a recording stylusadapted to trace a profile, wherein the means to integrate includes avoltage-to-frequency converter and a plurality of BCD cascade counters,wherein the means to select portions of the profile trace to beintegrated on rescan includes means to mark a medium on which thedensity profile trace is formed, and which includes means to control thescan and rescan cycles.
 6. The densitometer of claim 1 wherein the meansto rescan the sample includes holding means and drive means to move theholding means along a predetermined path, wherein the means to integratethe signal during rescan includes means to accumulate a plurality ofpulses on BCD cascade counters, wherein the means to compare the rescansignal with the total accumulated signal includes means to calculate thepercent of rescan signals compared against the total accumulated signal,and wherein the means to record the signal in digital form includesprint means.
 7. The densitometer of claim 6 wherein the means tocalculate the area percent includes a digital divider.
 8. Thedensitometer of claim 1 wherein the sample being analyzed is a thinlayer chromatography plate.
 9. The densitometer of claim 1 whichincludes means to define preselected areas of the analog trace.
 10. Animproved densitometer which comprises in combination: a. a source oflight energy; b. means to form a beam of said light energy; c. means toexpose a sample to be analyzed to the beam of light energy; d. means toscan the sample with the beam of light energy; e. means to convert thelight energy transmitted through the sample to an electrical signal; f.function generator means to convert the signal from the sample to alevel related to the amount of material to be analyzed in the sample; g.means to record the signal in analog form as a profile trace on arecording medium; h. means to integrate the selected signal with therecording of the selected signal in analog form in communication withthe function generator means; i. means to select a portion of the analogprofile trace from Which additional information is desired; j. means torescan the sample and to integrate the signal received; k. means tocompare the integrated rescan signal of the selected portion of theanalog profile trace with the total accumulated scan signal whereby oncomparison the pulses are discharged; and l. means to record thecompared signals in digital form on the medium.
 11. The densitometer ofclaim 10 wherein the function generator means includes a linear inverseconverter, a log inverse converter, function of x converter, and furtherincludes the means to record in one of said functions and integrate inthat or another of said functions as desired, wherein the mediumincludes chart recording means, and wherein the means to record indigital form includes:
 12. The densitometer of claim 11 wherein themeans to compare the integrated rescan signal against the totalaccumulated scan signal includes means to calculate percents.
 13. Thedensitometer of claim 12 wherein the means to calculate includes: meansto store a number representing the total amount of material; means tocontrol the movement of the holding means and bridge assembly means;means to control the selection of the information transmitted to thedigital printing means in the bridge assembly means; means to multiplypercent times the total amount of material; and means to print thepercent and the material amount for the selected portion of the analogtrace upon the receipt of a command from the sensing means.
 14. Thedensitometer of claim 10 wherein the sample being analyzed is anelectrophoresis strip.
 15. The densitometer of claim 11 wherein thebridge assembly means and the holding means for the sample are eachdriven by stepping motors which stepping motors are driven by pulsesderived from the same pulse train.
 16. A method of scanning a sample andrecording the results of said scan therefrom which comprises: a.creating a source of light energy; b. exposing a sample to be analyzedto the beam of light energy; c. receiving a portion of said beam oflight energy emerging from the sample on a receptor; d. converting thelight energy emerging from the sample to an electrical signal; e.integrating the electrical signal transmitted from the receptor; f.recording the signal from the receptor as an analog profile trace on amedium; g. selecting a portion of the profile trace from which desiredinformation is required; h. rescanning and integrating the sample overthe desired portion from which information is desired; i. comparing theintegrated rescan signal against the total integrated scan signal; j.providing a value representative of a comparison between the rescansignal against the total scan signal; and k. recording said value indigital form on the medium.
 17. The method of claim 16 which includesconverting the light energy emerging from the sample into an electricalsignal by transmitting said signal to a photometer; integrating saidsignal by converting the signal to a plurality of pulses andaccumulating the pulses.
 18. The method of claim 16 which includesrecording the signal from the photometer as an analog profile trace bytracing said signal on a recording medium, and further which includesselecting the desired portion of the profile trace from which additiOnalinformation is desired by marking the medium.
 19. The method of claim 16which includes converting the signal received on rescan into pulses andtotalizing the pulses received and further which includes dividingdigitally the pulses received on rescan by the pulses previouslyaccumulated during scan in a digital divider.
 20. The method of claim 16which includes printing the calculated value in digital form on themedium, and further which includes storing a material amount level,multiplying the value times said material amount level and recordingsaid calculations in digital form on the medium.
 21. The method of claim16 which includes: transmitting the electrical signal to one of aplurality of function generators, selecting the function in which theanalog trace is to be recorded, and selecting the function in which theintegration is made.
 22. The method of claim 21 wherein the functiongenerators include a log inverter, a linear inverter, and a function ofx converter.
 23. The method of claim 16 wherein the sample to beanalyzed is an electrophoresis sample.
 24. A modular computer forcalculating a fraction of a total area under a curve which comprises: a.means to receive signals representative of variations in composition ofa scanned sample from a source; b. means to display said signals inanalog form; c. means to integrate said signals; d. means to select aportion of the analog form from which additional information is desired;e. means to receive and integrate signals representative of variationsin composition of the sample rescanned; f. means to compare theintegrated rescanned signal with the integrated scanned signal; and g.means to record the compared signals in digital form.
 25. The computerof claim 24 wherein means to integrate the signals received includesmeans to accumulate a plurality of pulses on BCD cascade counters andwherein the means to compare the rescan signal with the totalaccumulated scan signal includes means to calculate the percent ofrescan signals compared against the total accumulated signal.
 26. Thecomputer of claim 24 wherein the means to display in analog formincludes a servomechanism in combination with a recording stylus adaptedto trace a profile, wherein the means to integrate includes avoltage-to-frequency converter and a plurality of BCD cascade counters,and wherein the means to select portions of the profile trace includesmeans to mark a medium on which the analog trace is formed.
 27. Thecomputer of claim 24 which includes: a. function generator means toconvert the signals received to a level related to the amount ofmaterial to be analyzed in the sample; b. means to record the signals inanalog form as a profile trace on a recording medium; c. means tointegrate the selected signals with the recording of the selectedsignals in analog form in communication with the function generatormeans; d. means to select a portion of the analog profile from whichadditional information is desired; e. means to compare the integratedrescan signals of the selected portion of the analog profile trace withthe total accumulated scan signals whereby on comparison the pulses aredischarged; and f. means to record the compared signals in digital formon the medium.